Means for neutralizing capacity coupling



June 5, 192s. y 1,672,641

J. F. DREYER, JR., ET AL' MEANS FOR- NEUTRALIZING CAPACITY COUPLING Filed Feb. 20, 1924 INVENTORS Jahw F. DHH/Hf, f/E.

u ATTORNEYS Patented June 5, 1928.

l 1,672,641 UNITED bSTATES PATENT OFFICE.

JOHN F. DREYER, JB., AND HARRYW. DREYER, F BROOKLYN, NEW YORK, ASSIGNORS,

BY MESNE ASSIGNMENTS, TO HAZELTINE CORPORATION, A CORPORATION OF DEL- AWARE.

MEANS FOR NEUTRALIZING CAPACITY COUPLING.

Application filed February 20, 1924. Serial No. 694,164.

This invention relates to electric condensers, and especially to condensers employed for the neutral-ization of capacity coupling in vacuum tube circuits. lt has tor its object more particularly the provision of a condenser of small electrostatic capacity and of an improved form and design, whereby a line and permanent adjustment of capacity may readily be attained. Such a device is of especialvalue in the neutralization of undesired capacity coupling in vacuum tube circuits such as described in Hazeltine United States Letters Patent Nos. 1,450,080, 1,489,228 and 1,533,858. l

A l'ine and accurate adjustment of etl'ective capacity o f condensers has heretofore been obtained in various ways, perhaps the most successful having been the mechanical micrometer or Verniertcontrol or, such as that utilized in the hihi-condenser. However, with the advent of vacuum tube receivers employing capacity neutralization there arose a need for a condenser of very small electro-static capacity, which could be accurately and finely adjusted over a narrow range, say from one to live micro-microfarads without the use of mechanical micrometer or vernier adjustments. It was therefore conceived that a condenser having a large ratio of length to capacity per unit length (i. e., one inch per ten micro microfarads) would enable extremely tine adjustment of its available eective capacity over a narrow, but still a suicient range.

To these ends a condenser of small size and of very small capacity is provided which possesses low losses and is capable of eX- tremely fine, accurate and permanent adjustment. The form of such acondenser may be tubular and comprise two electrodes, one within another, separated by a dielectric material of small surface area per unit length. The outer electrode under these conditions should be oftubular form and in order to facilitate the adjustment of the effective capacity thereof, one electrode may be movable or slidable axially relative to the other.

A more complete understanding of the present invention may be had from a consideration of the accompanying 'drawings together with the following description of i preferred embodiments as utilized in the neutralization of undesirable capacity coupling in vacuum tube radio receiving apparatus.

by any convenient means and which is pref` v erably tubular in shape, and an inside electrode 3 which may also be tubular, but which is preferably rodlike and may coinprise merely a short piece of heavy solid bare copper wire (for example Number 14 A. W. Gr. gauge) having a hole or hook 5 at one'end into which a connection wire (i may be secured by means of a binding post or by soldering or by any other convenient means. rlhe two electrodes are separated by a dielectric material 2, Which should have a high dielectric constant and low dielectric losses, such as possessed by glass, hard rubber, micanite, varnished cambric tubing and the like. The ratio of length to diameter of this dielectric tube may be conveniently about twenty to one.

, When small condenser-s of this type are used for neutralizing capacity coupling, it is usually desirable that the condenser be capable of-extremely close and accurate adjustment. For example, to neutralize the inherent capacity couplingl between the elements of a three electrode vacuum tube or audion, the capacity of the neutralizing condenser must bear a delinite ratio to the capacity of the audion; and to accomplish this result the electrodes of the condenser are made movable axially relative lto each other. Since the electro-static capacity of the condenser is proportional to the area of dielectric between the electrodes, it obviously is merely a matter of convenience how that adjustment is made, i. e., whether one or the other of the electrodes or the dielectric material is moved. Once the correct capacity isv determined, it is conveniently lined by means of sealing wax el, or other equivalent -means, which will loch the parts of the con-- denser against inadvertent movement; or in the case of completed radio receivers to 'be son 'to 'the publie, 'an absolutely faxed relation may be maintained by some more permanent means.

shows a modified form of the condenser illustrated in Fig. 1. -This embodiment 1s essentially similar to that above described, and comprises an-outer electrode 1, preferablyloftubular cross section; an inner electrode 3, which may consist of a short piece-,of heavy copper wire formed with a hole or a hook at one end, as shown at 5,

l securing it to auxiliary electrode 3",

so thatl it may be secured by screw 9 to an insulating base 8 and also asa means for connecting a conductor 6. Betwieen the electrodes is a dielectric material 2, which in-this embodiment may be varnished cambrlc tubing or other suitable insulating material. I-nner electrode 3 may fit-snugly into tubular` dielectric 2y in order that no other means need be used to prevent movement of the dielectric. Electrode 1 may be o-large enough inside diameter to allow of easy adshown in this figure of the drawing.

In order that the condenser may be of more convenient physical proportions and yet possess small capacit and ease of adjustment, a further modi cation of the condenser shown in Fig. -1 has been developed. This latter' form is illustrated in Fig. 3 which shows a condenser consisting of an 7 outside metallic electrode 1 which is prefer- -ternal and -by a ldielectric material 2 whlch electric loss,

ably tubular in shape, and two inside electrodes3 and 3a which, may 'also be tubular, but which preferably are rod-like and may lcomprise merely two short pieces of heavy, solid,'bare copper wire, for example #14 American gau e, having hooks 5 and at one end of eac electrode respectively, onto which'connection wires 6 may be secured by means of binding posts, or by soldering, or in any ,other convenient way. The inexternal electrodes are separated should high dielectric constant and low disuch as possessed by glass, ebonhave a ite, micanite, varni'shed cambric tubing and suggested. The ratio the like, as previously A of this dielectric tube of length to diameter may conveniently be about '20 to. 1.

It has been found that the capacity of this condenser may more readily be adjusted when one of the internal electrodes, for instance 3?, is longer Hman the other electrode', 3. By referring to `the figure, it will be noted that with this arrangement there is a comparatively greater electrostatic capacity between electrode`3iL and the external or intermediate electrode 1 than'there is'between electrode 1 and the shorter internal electrode 3. Thus the totalor eii'ective vcapacity value of the condenser is the resultant of two capacities in series, as just pointed out,l one capacity preferably being larger than the otherso that by sliding the external or intermediate electrode 1 axially with respect to the internal electrodes, one of these series capacities=is increased. while the other is decreased,'and a Very fine and accurate adjustment of the effective resultant capacit-y between the connecting wires 6-6 may be had. By this arrangement, also, the resultant capacity may bey very small, as required, and yet the physical vsize of the unit may be sufciently large to perj v mit of easy handling. The strap or clamp, shown in the figure, held in place by 'screw l0, has been found to be a convenient means for locking the external electrode 1 in position after the neutralizing adjustment has been obtained. In commercial practice, it has been found expedient to solder the locking strap to the intermediate electrode in order that the neutralizing adjustment may not be tampered with.v The dielectric tube 2 is preferably held in fixed relation to the insideelectrodes by means of sealing wax 4, altho frequently these electrodes lit the dielectric tube so tightly that no additional xing means is necessary. Likewise, it is sometimes desirable, instead of'fixing` the external electrode by means of av clamping device as shown at 10, to split or slot the electrode so that it will engage frictionally .with the dielectric tube.

By referring to the figures, it will be observed that the condenser structure provided by the present invention results in a condenser which allows of extremely fine and accurate 'determination of its capacity value without including expensive mechanical m1- in billlwire; the dielectric tubing required being also readily available onv the market without further machining. Furthermore, it maybe pointed out that the present invention provides a condenser structure which is extremely permanent in capacity adjustment because all of the separate parts of the condenser are supported thruout the greater portion of their-length, so that the is' a mechanically rigid structure whichA can not be inadand 3*l fit snuglIy7 inside dielectric tube 2 thru- 3 tube of circular out substantial their entire length and thus are rigidly sup orted. The screws 15 and 15Il are servicea le in functioning as bindin posts for external connecting wires as we l as for assisting clamp 10 in holding the entire condenser rigidly to the base plate 8. Conse uently, there is no unsupported por-1 tion o the condenser which may be moved by heavy vibration or mechanical shock which, in prior forms of condensers, would tend to change 'the capacity adjustment of the device. Y

In the foregoing description of certain preferred embodiments of-this invention, the inside electrodes-have been conveniently represented as com rising rodlike members, the

outside electro e as comprising a metallic tric material as comprising a tubular memto which it maybe 'tube and adjustab cross section, and the dielecber of circular cross section, but it is to be understood that modifications in the general proportions, shape and cross section of these members may be necessary in adapting the invention to other specific applications without in any way departing from the spirit or' sccge of the invention.

e claim:

A condenser structure capable of fine and permanentl adjustment of its electrostatic ca acity, comprising tworod-like electrodes o different lengths, inserted one from either end of an insulating dielectric tube,

said electrodes fitting snugly in said tube and being not in electrical contact with each other, an intermediate tubular metallic electrode fitted snugl outside said dielectric e longitudinally of said dielectric tube, an insulating base-plate for said structure and a lurality of means for securing said con enser to said baseplate and for making electrical connectionsy to said two rod-like electrodes whereby the elements of said condenser are at all required adjustments rigidly supported thruout the greater part of their lengths, and ease and permanence of adjustment are attained.

In testimony whereof we aiiix our signatures.

JOHN F. DREYER, JR. HARRY w. DREYER. 

